A SINGLE-CHAIN ANTIBODY (SCA) PROTEIN WITH SPECIFICITY FOR HUMAN IGM WILL BE PREPARED. THE SCA PROTEIN WILL BE DESIGNED FROM THE VARIABLE REGIONS OF THE ANTIHUMAN IGM MONOCLONAL ANTIBODY, DA4.4. A GENE TO SYNTHESIZE THIS PROTEIN WILL BE CONSTRUCTED, AND THE PROTEIN WILL BE EXPRESSED IN ESCHERICHIA COLI. THE PROTEIN WILL BE FOLDED, PURIFIED, AND ASSAYED FOR ITS BINDING TO HUMAN IGM. THIS PROTEIN WILL BE USED AS A REAGENT FOR THE PURIFICATION OF HUMAN IGM ANTIBODY AND HUMAN IGM MONOCLONAL ANTIBODIES; AS A DIAGNOSTIC REAGENT FOR ANTIGEN-SPECIFIC IGM; AND AS A THERAPEUTIC IN EXTRACORPOREAL BLOOD FILTRATION FOR DISEASES,E.G., CANCER AND AIDS. THE IMMOBILIZATIONS NECESSARY FOR THIS PROTEIN TO PERFORM IN THESE REACTIONS WILL BE DEVELOPEDDURING PHASE II.